As the title describes, if one owns the Galaxy Nexus, then they have an example of the product in their possession already. I can confirm that the product is genuine (my order was fulfilled by Amazon, rather than coming direct) and at approximately £15, it represents reasonably good value and allays fears that Samsung's decision to build NFC into the device's battery would result in expensive replacement batteries. I would happily purchase another at this price if my situation called for it.
Although there isn't much more to say about what is essentially a consumable. It may be some help to list some of the scenarios that motivated me to buy a second battery.
To remove the issue wear on the original battery as a factor for replacing my device. A great scenario to be if one intends to keep their device for 2 years, and not have such an issue force them to adopt a new device
To allow total depletion of the devices battery "in the field". I may not need to use a second battery very often. But one of the core benefits is to allow the primary battery run down to zero, rather than having to nurse the device when the battery hits 30% in order to receive calls and texts, sending the devices functionality from smart to dumb. Having a spare battery on hand allows the user to be a little bit less conservative with the phone's use, even if they don't use the second battery
Freedom from the charger, with 2 batteries, with my standard usage, I can avoid putting my device anywhere near a charger for 3 days, and with a dedicated battery charger, simply by cycling the batteries it allows the user to never plug their phone into the mains again.
and finally, the super heavy usage scenario, I can't imagine a scenario where in the 9 or so hours that I am away from my charger, I'll rip through 3500mah, but it's nice to have peace of mind.
Thanks for reading